Characterization of Urtica dioica agglutinin isolectins and the encoding gene family

Urtica dioica agglutinin (UDA) has previously been found in roots and rhizo mes of stinging nettles as a mixture of UDA-isolectins. Protein and cDNA se quencing have shown that mature UDA is composed of two hevein domains and i s processed from a precursor protein. The precursor contains a signal pepti de, two in-tandem hevein domains, a hinge region and a carboxyl-terminal ch itinase domain. Genomic fragments encoding precursors for UDA-isolectins ha ve been amplified by five independent polymerase chain reactions on genomic DNA from stinging nettle ecotype Weerselo. One amplified gene was complete ly sequenced. As compared to the published cDNA sequence, the genomic seque nce contains, besides two basepair substitutions, two introns located at th e same positions as in other plant chitinases. By partial sequence analysis of 40 amplified genes, 16 different genes were identified which encode sev en putative UDA-isolectins. The deduced amino acid sequences share 78.9-98. 9% identity. In extracts of roots and rhizomes of stinging nettle ecotype W eerselo six out of these seven isolectins were detected by mass spectrometr y. One of them is an acidic form, which has not been identified before. Our results demonstrate that UDA is encoded by a large gene family.